A realistic model of the major pathways of intermediary metabolism in Tetrahymena pyriformis will be written, incorporating all the known data on which enzymes are present and in which intracellular compartments they are localized. Equations will be written that allow one to compute the specific activity of every carbon atom of every metabolite in the system in the steady state for C14 labeled input from any labeled substrate that it is intended to make measurements with. Cells grown under carefully controlled conditions will be exposed to a suitable mixture of substrates so that all flasks are in the identical metabolic state. Each flask, however, will have one of the substrates present labeled in a specified position. Measurements will be made under steady (or quasi-steady state) conditions of label incorporated from each labeled substrate into lipids, glycogen, CO2, and other products as required, so that there will be a considerable excess of measurements to flux rates to be determined, thereby permitting a stringent test of the model. A fit to the data will be attempted, using a suitable computer program of the steady state equations. Achievement of a fit will then yield a quantitative description of the flux of metabolites along all the major pathways of intermediary metabolism for this cell. Similar experiments will be done in the presence of L-propanolol and cyproheptadine to gain understanding of the operation of the "primitive" adrenergic and serotoninergic metabolic control system of this ciliate. Experiments will also be done to set up a comparably realistic model for rat hepatocytes and then to test this model and use it for a study of the effects of glucagon on the metabolite flux pattern.